Asymmetric pole pieces for color kinescope convergence cage



Aug. 25, 1970 JAVORIK ET AL ASYMMETRIC POLE! PIECES FOR COLOR KINESCOPECONVERGENCE CAGE Filed 001;. 22, 1968 United States Patent 3,525,892ASYMMETRIC POLE PIECES FOR COLOR KINESCOPE CONVERGENCE CAGE LaszloJavorik, Chicago, George A. Rokos, Westchester,

and Benjamin L. Gelfand, Chicago, Ill., assignors to National VideoCorporation, Chicago, Ill., a corporation of Illinois Filed Oct. 22,1968, Ser. No. 769,513 Int. Cl. Hlllj 29/54, 29/72 US. Cl. 313-77 3Claims ABSTRACT OF THE DISCLOSURE The two lower side pole pieces in themagnetic con- Vergence cage of a three-beam gun for a color kinescope ofthe shadow mask type are modified to provide asymmetric deflection loci.The deflection loci for the two side beams are directed above the axisof the convergence cage and thus correct for errors in verticaldisplacement of the converged beams due to the unequal vertical locationof the beams relative to the axis of the convergence cage.

BACKGROUND AND SUMMARY The present invention relates to multiple-beamcolor kinescopes of the shadow mask variety; and more particularly, itrelates to an improved magnetic convergence cage for a color kinescope.

A conventional color kinescope of the shadow mask type has a glass neckportion at one end, a faceplate (on which is formed an enlarged viewingscreen) at the other end, and a funnel-shaped portion joining theconstricted neck portion with the faceplate panel. Three guns (i.e.sources of electron beams) are arranged in delta array in theconstricted neck portion of the tubethat is, in cross section, thecenters of the three beams define an equilateral triangle and the centerof the triangle is coincident with the axis of the constricted neckportion of the tube. Each electron beam is modulated with a video signalrepresentative of a different primary color in the image beingreproduced.

An apertured shadow mask is mounted within the tube envelope adjacentthe viewing screen; and each aperture in the shadow mask is associatedwith a triad of the mosaic of color-producing phosphor dots deposited onthe interior of the faceplate panel which comprises the viewing screen.Each of the phosphor dots of a triad produces a different primary color(for example, red, green, and blue); and each dot is, in turn, energizedby that electron beam which is modulated by the video signalrepresentative of the color component reproducible by that dot. Colorseparation is attained by converging the three beams at the shadow maskso that as the beams pass through an aperture, they cross and strikeonly their associated color-producing phosphor dots. The triads of thephosphor mosaic are interlaced so that the three images appear as one tothe eye.

A conventional dynamic convergence cage for converging the beams has acircular plate mounted to the final electrode of each of the threeelectron beam guns; and this plate defines three equally-angularlyspaced apertures through which the three separated electron beams flow.A cylindrical flange or wall member extends downstream (i.e. toward theviewing screen) from, and is integral with, the circular plate; andthere are two elongated slots extending axially of the cylindrical wallmember for each of the beams passing through the cage.

A magnetic pole piece is fitted into each of the slots so that a pair ofmagnetic pole pieces is associated with P CC each of the beams. Each ofthe pole pieces has a recep tion portion which generally conforms to theshape of the cylindrical wall member and is located externally thereoffor receiving the dynamic convergence signal from a magnetic deflectioncoil. Each pole piece then extends interior of the cage and provides apole face adjacent its associated electron beam. The pair of pole facesfor each beam are located on opposite sides of the beam; and theycooperate to establish a magnetic field transverse of their associatedelectron beam for deflecting the same radially inward of the cylindricalwall of the cage toward its axisthus, conventional deflection loci aresymmetrical relative to the axis of the convergence cage.

In conventional magnetic deflection schemes for dynamic convergence, aseparate convergence coil is supplied exterior of the constricted neckportion of the tube for energizing each of the pairs of pole pieces.These deflection coils are normally spaced at angular degrees about theconstricted neck portion of the tube; and each pair of pole pieces, whenenergized by its associated deflection coil sets up a center line ofdeflection force for its beam. All three of these deflection linesnormally coincide with the axis of the convergence cage-- that is, thecenter of deflection is a point at center of equilaterial triangledefined by the beams.

Since the top beam is situated directly over the center, the deflectionforce exerted on the top beam is vertically downward. The other twobeams, being located beneath and to the sides of the axis of theconvergence cage, are deflected toward the axis at angles of 30 from thehorizontal. Hence, for the same deflection force exerted on each of thebeams, the vertically downward deflection (that is, the verticalcomponent of deflection only) of the top beam will be much greater thanthe corresponding vertical component of the deflection of the sidebeams. Thus, in order to converge, the top beam experiences a muchgreater vertical displacement component relative to the center ofdeflection than to the side beams. A balanced correction is madediflicult by this greater vertical component of deflection in the topbeam.

According to the arrangement of the present invention, the two sidebeams are caused to be deflected upwardly at a greater angle relative tothe horizontal (for example, at a 60 angle) so that the upwarddeflection of these beams more nearly equals the downward deflection ofthe top beam. Reference will sometimes be made herein to the deflectionlocus of the beams, and this refers to the straight-line direction inwhich the beams are forced in a plane perpendicular to the flow ofelectrons by the convergence cage. Thus, according to the presentinvention, the center lines of the deflection force for the side beamsno longer meet at the axis of the cylindrical wall of the convergencecage; rather, they meet at a point above the axis of the cylindricalcage wall so that the vertically upward deflection of the side beams ismore nearly equal to the vertically downward deflection of the top beam.In other words, the center of deflection is translated directly upward,and the pole piece arrangement becomes asymmetric relative to the axisof the cage.

This result is accomplished without changing the equilateral trianglearray of the three beams and without changing the angular disposition ofthe magnetic deflection coils exterior of the constricted neck portionof the tube.

Other features and advantages of the present invention will be apparentto persons skilled in the art from the following detailed description ofa preferred embodiment accompanied by the attached drawing whereinidentical reference numerals will refer to like parts in the variousviews.

3 THE DRAWING FIG. 1 is a partially cut-away view of the electron beamguns in the constricted neck portion of a color kinescope incorporatingthe present invention;

FIG. 2 is a transverse cross section view taken through the sight line22 of FIG. 1;

FIG. 3 is an enlarged detail cross section view of the improvedconvergence cage of the kinescope of FIG. 2; and

FIGS. 4-5 are enlarged perspective views of separate pole piecesincorporated in the convergence cage of the kinescope of FIG. 2.

DETAILED DESCRIPTION Referring now to FIG. 1, a glass envelope of theconstricted neck portion of a color kinescope of the shadow mask type isgenerally designated by reference numeral 10. At the base (or upstreamend) of the neck (that is, the left-hand end as viewed in FIG. 1), aplurality of terminal pins 11 are fed through the glass envelope 10 forcoupling suitable filament and grid voltages to the various electrodes,presently to be described.

These are three separate sources of electron beams, commonly referred toas guns in the constricted neck portion of the tube envelope; and thethree beams flow parallel to the axis of the neck. In cross section, thecenters of the three beams define an equilateral triangle, the center ofwhich is coincident with the axis of the neck. Although not illustratedin the drawing, a funnel portion of the tube envelope is formedintegrally with the neck portion and extends outwardly thereof. Afaceplate panel is joined at the enlarged end of the funnel; and aconventional apertured shadow mask is mounted inwardly of the faceplatepanel. These elements are not illustrated since they are conventional,and the present invention may be fully understood by persons of ordinaryskill in this art without describing such elements in further detail.

Each of the three electron guns, arranged in delta array, issubstantially identical to the others; and therefore, only one of theguns will be described in greater detail here. Referring to FIG. 1 andin particular to the lower left hand gun as seen in FIG. 2, a firstcylindrical grid 12, commonly referred to as grid I or the control grid,is mounted about a conventional cathode assembly (not shown) which ismechanically supported within, but electrically isolated from, theconductive electrode 12. Proceeding downstream of the beam from thecontrol grid 12, there are three other electrodes arranged in order andgenerally designated by reference numerals 13, 14, and 15 respectively.These three grids are commonly referred to as the screen grid, the focuselectrode, and the anode. Each of the electrodes 12-15 associated withone of the electron guns is located coaxially with respect to the beamit generates; and the center of each defines an aperture to permitunrestricted passage of the electron beam.

As is also conventional, the three guns are rigidly mounted as a unit bymeans of supporting straps, the ends of which are secured in elongatedglass beads such as the one shown at 16. Each strap has one end mountedin a bead, then is formed into a circular portion which is welded to anassociated cylindrical electrode, and has its second end mounted in asecond bead spaced about the interior of the neck portion. Thus, allthree guns form a rigid structure supported within the constricted neckportion 10 of the tube envelope by three glass supporting rods or beads.

All three beams, after exiting from the accelerating anodes 15, are fedinto a convergence cage which includes a cup-shaped member generallydesignated 18 and including a circular plate 19 (see FIGS. 2 and 3)adjacent the anodes 15, and a cylindrical side wall 20 integral with andextending downstream from the plate 19. The con- 4 vergence cage 18 isat the same electrical potential as the anode 15.

Referring now to FIGS. 2 and 3, three apertures permitting passage ofthe three beams are provided in the circular plate 19; and these threeapertures are designated respectively by reference numerals 21, 22, and23. As mentioned, the electron beams are arranged in delta array; and sothe centers of the apertures 21-23 define an equilateral triangle havingits center at the axis of the cylindrical side wall 20. The convergencecage, in end view, is divided into three equal wedge segments by aY-shaped separator 26.

Three magnetic deflection coils designated respectively 28, 29 and 30 inFIG. 2 are mounted exterior of the constricted neck 10 adjacent theconvergence pole pieces of the three beams respectively. As seen in FIG.2, the magnetic deflection coils 2830 have one pole face respectively oneach side of radial lines passing through the apertures 2123. Thesedeflection coils are energized by dynamic convergence signals which aregenerated according to known technique as the three beams scan a rasteron the image screen. Heretofore, the deflection locus of each of thebeams was symmetrically toward the axis of cage.

Further details concerning the structure and operation of convergencepole pieces in color kinescopes may be obtained from the co-pending,co-owned application of Javorik et al., for Improved Convergence 'Cagefor Color Kinescope, Ser. No. 722,581, filed Apr. 19, 1968.

The cylindrical wall member 20 is provided with a plurality of elongatedslots extending parallel to its axis for receiving the convergence polepieces; and there are two such pole pieces associated with each of thebeam apertures 21-23.

Received in each of the slots 31 in the cylindrical wall 20 1s amagnetic pole piece. The two pole pieces associated with the aperture 21are generally designated 33 and 34 in FIG. 3. Each of the pole pieces 33and 34 is similar; and they are symmetrical about a vertical radial linepassing through the axis of the cylindrical wall 20. The pole piece 33has a reception portion 35 welded to the exterior surface of the wallmember 20 and extending beneath one of the poles of the deflection coil28 and a lower, detented pole face 36 extending to the left side of theaperture 21. Similarly, the pole piece 34 has a reception portion 38lying beneath the other pole of the deflection coil 28 and a pole face39 lying adjacent the beam passing through the aperture 21.

The pole faces 36 and 39 of the pole pieces 33 and 34 face each other;and it is across these opposing pole faces that the magnetic field isgenerated to deflect the beam passing through the top aperture 21 in adownward directron relative to the center of the three beams. The lineof magnetic deflection force exerted by the magnetic field generatedacross the pole faces 36 and 39 is illustrated by the chain line 40 inFIG. 3.

The pole pieces deflecting the electron beam passing through theaperture 22 are generally designated by reference numerals 41 and 42.The pole piece 41 is provided with a reception portion 43 welded to theexterior surface of the cylindrical wall 20; and it includes a pole faceportion 44 which is again provided with a detent, although these are notnecessary for operation. Similarly, the pole piece 42 has a receptionportion 45 and a pole face 46. The reception portions 43 and 45 of thepole pieces 41 and 42 receive the magnetic field generated by thedeflection coil 29 and generate a magnetic deflection force across thepole faces 44 and 46; however, in this case, the pole faces 44 and 46are arranged so that the center line (deflection locus) along which themagnetic deflection force is exerted displaces the center of the beamflowing through the aperture 22 along the chain line 49. It will beappreciated that the deflection locus does not force the electron beampassing through the aperture 22 directly toward the axis of thecylindrical wall 20, but along a locus inclined slightly above it. In apreferred embodiment, the deflection lines of the two lower convergencepole pieces form a 30 angle on either side of a vertical line which liesalong the deflection locus of the upper convergence pole piece.

Turning now to the pole pieces associated with aperture 23, referencenumerals 50 and 51 generally designate these pole pieces. The pole piece50 forms a mirror image of the previously-described pole piece 41; andit includes a reception portion 52 and a pole face 53. Similarly, thepole piece 51 is a mirror image of the previously-described pole piece42, and it includes a reception portion 55 and a pole face 56. Thereception portions 52 and 55 receive the magnetic field generated by thedeflection coil 30; and the pole faces 53 and 56 cooperate to deflectthe beam passing through the aperture 23 along a locus indicated by thechain line 57. If extended, the deflection loci 49 and 57 for the lowerside beams would intersect at a point above the axis of the cylindricalwall 20 of the convergence cage. For this reason, the cage is sometimesreferred to as asymmetric.

Turning now to FIG. 4, the configuration of the pole pieces 42 and 51 isseen in perspective view; and it will be appreciated that the sameconfiguration is interchangeable for each of these poles by turning themember endon-end. In FIG. 4, the reception portion of the pole piece isdesignated 60; and the pole face is generally designated til. FIG. showsa similar view of a pole piece which may interchangeably be used foreither of the previously-described pole pieces 43 or 52 by, again,turning it end-on-end. In FIG. 5, the reception portion is generallydesignated 62, and the pole face which extends adjacent the beamaperture in the plate 19 is generally designated by reference numeral64.

With the pole piece thus arranged, it can be seen that the deflectionlocus for the beam passing through the top aperture 21 remains directlydownwardthat is, toward the axis of the cylindrical wall At the sametime, the deflection loci defined by the pole faces for the beamspassing through the lower side of the aperture are more steeply inclinedupwardly than heretofore; and they meet at a point above the axis of thecylindrical wall 20 to cause the vertically upward deflections of theside beams to be more nearly equal to the vertically downward deflectionof the top beam-thus reducing the vertical displacement error caused inconverging the blue (top) beam at the shadow mask or on the viewingscreen.

Having thus described in detail a preferred embodiment of the improvedconvergence cage, persons skilled in the art will readily conceive ofvariations in pole piece configurations which may be substituted for theparticular ones described and yet which practice the inventiveprinciple; and it is, therefore, intended that all such modificationsand substitutions be covered as they are embraced within the spirit andscope of the appended claims.

We claim:

It. in a three-beam color kinescope having a shadow mask adjacent amosaic of phosphor dots on the viewing screen and a magnetic deflectioncoil for dynamically converging each of said beams, an improvedconvergence cage comprising: a cylindrical wall member in theconstricted neck of said kinescope and defining a pair of elongatedslots for each beam, each pair of slots lying adjacent a pole of itsassociated magnetic deflection coil; a circular plate member integralwith the upstream edge of said cylindrical wall member and defining anaperture for the passage of each of said beams, the centers of saidapertures disposed at equal angular increments about the axis of saidwall member, and a center of one of said apertures lying directly abovesaid axis, the other centers of said apertures lying beneath and to therespective sides of said axis; a first pair of magnetic pole piecesreceived in a first pair of slots of said cylindrical wall member andincluding opposing pole face members on opposite sides of said topaperture, said pole faces of said first pair of pole pieces defining adeflection locus extending along a line from the center of said topaperture through the axis of said cylindrical wall member; a second pairof magnetic pole pieces received in a second pair of said slots andincludin pole faces extending on either side of a second beam passingthrough a second of said apertures, said second pair of pole facesacting to define a deflection locus for said second beam extending fromthe center of said second aperture to about the center of said topaperture: and a third pair of pole pieces received in said third pair ofslots and providing a pair of pole faces on either side of said thirdaperture, said third pair of pole pieces cooperating to define adeflection locus for said third beam along a line extending from thecenter of said second aperture to about the center of said top aperture.

2. The convergence cage of claim 1 wherein said wall member defines aslot extending generally axially thereof for receiving an associatedpole piece, the reception portions of each of said pole pieces generallyconforming to and welded to the exterior surface of said convergencecage, said deflection coils being spaced at 120 separations about saidconstricted neck portions.

3. The convergence cage of claim 2 wherein the extensions of thedeflection loci defined by said pole pieces associated with said sidebeams intersect at an axial extension of the center of said top apertureand thereby form an angle of References Cited UNITED STATES PATENTS2,847,598 8/ 1958 Hughes.

FOREIGN PATENTS 259,640 1/1968 Austria.

ROBERT SEGAL, Primary Examiner US. Cl. X.R. 313-

